1. Field of the Invention
The present invention relates to an ink jet recording sheet having excellent gloss and ink jet recording ability. More particularly, the present invention relates to an ink jet recording sheet having excellent gloss and ink jet recording ability and a high resistance to damage to the front surfaces of the recording sheets by sheet-conveying rollers arranged in a sheet-feeding section of the ink jet printer.
2. Description of the Related Art
The recording by an ink jet printer is advantageous in that the printing noise is low, high speed printing can be done and multi-color printing is easy, and thus ink jet printers are utilized in many fields. As a sheet for the ink jet recording, various woodfree paper sheets having an improved ink-absorbing property and various coated paper sheets having a front coating layer comprising porous pigment particles are used. For example, Japanese Unexamined Patent Publication No. 62-158,084 discloses a process for producing an ink jet recording paper sheet having a front coating layer containing fine porous synthetic silica particles and exhibiting a high ink-absorbing property and a high color density of the printed ink images.
Conventional recording paper sheets are, however, generally low gloss ink jet recording sheets having a mat surface and thus cannot record thereon full colored images having a photographic-image-like tone. Accordingly, an ink jet recording sheets having a high surface gloss and an excellent appearance are currently in demand.
Generally, as a high surface gloss paper sheet, a high gloss coated paper sheet produced by coating a support sheet surface with a plate-crystalline pigment, and optionally calendering the pigment coated surface, or a cast-coated paper sheet produced by bringing a wetted resin coating layer on a support sheet into a contact under pressure with a mirror-finished surface of a heated casting drum and drying the coating layer, to transfer the casting mirror surface to the coating layer, are known.
The cast-coated paper sheet has excellent surface gloss and smoothness and exhibits a superior printing effect in comparison with those of the conventional pigment-coated paper sheet, and thus is employed only for high grade prints. When used for ink jet recording, the cast-coated paper sheet is disadvantageous in various ways.
Generally, the usual cast-coated paper sheet is disclosed in, for example, U.S. Pat. No. 5,275,846. In this case, the cast-coated layer is formed from a composition comprising a pigment and a film-forming substance, for example, a binder. The film-forming substance enables the cast-coated layer to transfer the mirror-finished casting surface to the cast-coated layer, and thus the resultant cast-coated layer has a high gloss. However, the film-forming substance causes the porosity of the cast-coated layer to decrease and thus the resultant cast-coated layer exhibits a very low ink-absorbing property for the ink jet printing. To improve the ink-absorbing property, the porosity of the cast coated layer must be increased so as to enable the cast-coated layer to easily absorb the ink. For this purpose, the content of the film-forming substance in the cast-coated layer must be decreased. When the content of the film-forming substance is decreased, the resultant cast-coated layer exhibits a reduced gloss.
As mentioned above, it is extremely difficult to provide a cast-coated paper sheet satisfactory in both a high surface gloss and a high ink jet printing ability.
As a means for solving the above-mentioned difficulty, European Unexamined Patent Publication No. 634283A discloses an ink jet recording sheet produced by a process in which a support paper sheet surface is coated with an undercoat layer comprising, as principal components, a pigment and a binder; the undercoat layer surface is coated with a coating liquid containing, as a principal component, a composition of a copolymer of ethylenically unsaturated monomers and having a gloss transition temperature of 40.degree. C. or more, to form a coating liquid layer for a cast-coated layer; and the coating liquid layer in a wetted condition is brought into contact under pressure with a mirror-finished surface of a heated casting drum, and dried. By this process, the resultant cast-coated paper sheet has both an excellent gloss and a superior ink-absorbing property, and is useful as an ink jet recording sheet.
The above-mentioned process enables the ink jet recording sheet having excellent surface gloss and ink jet recording aptitude to be produced. However, the resultant ink jet recording sheet having a high gloss, particularly a 75 degree gloss of 30% or more determined in accordance with JIS Z 8741, is disadvantageous in that, when the recording paper sheet is conveyed within the printer, the front surface of the recording sheet is damaged by sheet-conveying-rollers equipped with sheet conveying gears or spurs, and the resultant gear or spur marks on the recording sheet are easily recognized.
Particularly, the current ink jet printers have a fine and precise mechanism and thus can record photographic image-like ink jet images. However, to enhance the sheet-conveying accuracy of the printers, there is such a trend that the number of the gears or spurs attached to the sheet-conveying rollers is increased, and thus the gear or spur marks are formed more easily.
As mentioned above, in the ink jet printer, the printed recording sheet is conveyed by sheet-conveying rollers equipped with sheet-conveying metallic gears or spurs in such a manner that the printed recording sheet, which has been locally swollen with the printing ink and thus has been softened as a whole, is brought into contact under pressure with the metallic gears or spurs, and thus obvious gear or spur marks are formed on the printed recording sheet. Thus, there is a strong demand of solving the gear or spur mark problem on the recording sheet.